4
R.G. Lawford
somewhat symmetrical about the equator. However , asymmetries also
exist. The nature of these symmetries and asymmetries and their consequences for the distribution of water resources and ecosystems along
these coasts are examined here . Some aspects of this work are refinements
of the ideas and preliminary data reported by Lawford (1993).
Overview of Hydrometeorological Patterns and Processes
Solar radiation, soil moisture, and nutrient supplies are all factors that
influence ecosystem productivity and function. From an ecosystem perspective, precipitation is the most critical hydrometeorological parameter,
because it determines the moisture availability and, together with surface
geomorphology, controls runoff, river discharge, sediment transport, and
nutrient cycling. Soil moisture and subsurface water movement are
important related parameters and can influence biome characteristics.
Waring and Schlesinger (1985) suggest that the ability of soils to provide
moisture to plants during long drought periods is one of the major natural
factors promoting forest growth over grasslands.
Temperature and insolation determine the rate of plant growth and,
together with moisture availability, control biomass productivity. Plant
functionality and biodiversity are dependent upon these parameters and
their seasonal and interannual variations. Clouds play an important role
in regulating insolation and generating precipitation.
Symmetry and Asymmetry
There are a number of reasons to anticipate significant symmetries between North and South America. First, the regular oscillation in the tilt
of the earth's axis with a summer solstice in June when the sun reaches its
zenith at 22.5°N, and a winter solstice in December when the same
occurs at 22.5°S, should be conducive to symmetrical seasonal cycles in
both hemispheres . Furthermore, the coastal ocean currents are similar,
with the Antarctic drift current bifurcating as it reaches the shores
of Chile near 51°S and the North Pacific current bifurcating west of
Vancouver Island at approximately 49°N. A nearly continuous chain of
mountains extends from Alaska in the north to the southern tip of Chile.
In addition , the hemispheres have similar wind regimes, with strong
westerly winds at mid-latitudes (30° to 55° in winter and 35° to 60° in
summer) interacting with a mountain chain to produce higher precipitation amounts on the windward side of the mountains along the coast.
However , it should be noted that winds in the Northern Hemisphere tend
to undergo larger seasonal variations , with lower wind speeds in the
summer.
It would be very surprising to find complete symmetry in these comparative analyses, in spite of the fact that the two regions show arguably
R.G. Lawford
somewhat symmetrical about the equator. However , asymmetries also
exist. The nature of these symmetries and asymmetries and their consequences for the distribution of water resources and ecosystems along
these coasts are examined here . Some aspects of this work are refinements
of the ideas and preliminary data reported by Lawford (1993).
Overview of Hydrometeorological Patterns and Processes
Solar radiation, soil moisture, and nutrient supplies are all factors that
influence ecosystem productivity and function. From an ecosystem perspective, precipitation is the most critical hydrometeorological parameter,
because it determines the moisture availability and, together with surface
geomorphology, controls runoff, river discharge, sediment transport, and
nutrient cycling. Soil moisture and subsurface water movement are
important related parameters and can influence biome characteristics.
Waring and Schlesinger (1985) suggest that the ability of soils to provide
moisture to plants during long drought periods is one of the major natural
factors promoting forest growth over grasslands.
Temperature and insolation determine the rate of plant growth and,
together with moisture availability, control biomass productivity. Plant
functionality and biodiversity are dependent upon these parameters and
their seasonal and interannual variations. Clouds play an important role
in regulating insolation and generating precipitation.
Symmetry and Asymmetry
There are a number of reasons to anticipate significant symmetries between North and South America. First, the regular oscillation in the tilt
of the earth's axis with a summer solstice in June when the sun reaches its
zenith at 22.5°N, and a winter solstice in December when the same
occurs at 22.5°S, should be conducive to symmetrical seasonal cycles in
both hemispheres . Furthermore, the coastal ocean currents are similar,
with the Antarctic drift current bifurcating as it reaches the shores
of Chile near 51°S and the North Pacific current bifurcating west of
Vancouver Island at approximately 49°N. A nearly continuous chain of
mountains extends from Alaska in the north to the southern tip of Chile.
In addition , the hemispheres have similar wind regimes, with strong
westerly winds at mid-latitudes (30° to 55° in winter and 35° to 60° in
summer) interacting with a mountain chain to produce higher precipitation amounts on the windward side of the mountains along the coast.
However , it should be noted that winds in the Northern Hemisphere tend
to undergo larger seasonal variations , with lower wind speeds in the
summer.
It would be very surprising to find complete symmetry in these comparative analyses, in spite of the fact that the two regions show arguably